Method for manufacturing biodegradable packaging material, biodegradable packaging material and a package or a container made thereof

ABSTRACT

A biodegradable packaging material, a method of manufacturing the same, as well as products made of the material wherein the manufacture comprises extrusion onto a fibrous substrate one or more polymer coating layers including at least one layer of a polymer blend consisting of (i) 20-95 wt-% of polylactide having a high melt index of more than 35 g/10 min (210° C.; 2.16 kg), (ii) 5-80 wt-% of polybutylene succinate (PBS) or a biodegradable derivate thereof, and (iii) 0-5 wt-% of one or more polymeric additives. The components of the blend are melted and blended in connection with the extrusion step. The goal is to improve extrudability, increase machine speed in extrusion and maintaining good adhesiveness to the substrate and good heat-sealability of the coating. The products include disposable drinking cups and board trays, as well as sealed carton packages for solids and liquids.

RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No. 14/438,139filed Apr. 23, 2015, now U.S. Pat. No. 10,167,594, which is a NationalPhase entry of PCT Application No. PCT/FI2013/051015, filed Oct. 28,2013, which claims priority from Finland Application No. 20126113, filedOct. 26, 2012, the disclosures of which are hereby incorporated byreferenced herein in their entirety.

FIELD OF THE INVENTION

The present invention is generally related to a method of manufacturinga biodegradable packaging material comprising extrusion onto a fibroussubstrate one or more polymer coating layers. The present invention isalso generally related to biodegradable packaging material obtained bysaid method as well as containers and product packages comprising thepackaging material according to the present invention.

BACKGROUND OF THE INVENTION

The fibre-based packaging material of product packages, such as packingpaper or board, is usually provided with a polymeric coating that makesthe package tight and allows closing the package by heat sealing.Similar polymer-coated paper or board is also used for disposabletableware, such as drinking cups. Polyolefins, such as low-densitypolyethylene (LDPE), are widely used for coating due to their goodheat-sealability. A disadvantage of the usual polyolefins is, however,that they are not biodegradable.

Polylactide (PLA), which has reasonably good moisture and gas barrierproperties that are sufficient to many applications, has been used asthe coating polymer of biodegradable packaging material; however, itsuse involves a number of problems. Standard low melt index polylactideis stiff and fragile, requiring a high extrusion temperature and afairly large layer thickness to stick to the fibre substrate of thepackaging material. Because of the high temperature, such polylactideruns the risk of deterioration, and in extrusion, the edges of a moltenweb tend to tear and pin holes easily remain in the extruded layer. Thisalso results in a low machine speed.

To solve the extrusion problems, EP-1094944 B1 discloses an inneradhesion layer, which is coextruded together with an outer polylactidelayer, and which consists of a biodegradable polymer, examples of which,according to the specification, include some commercial copolyesters,cellulose esters, and polyester amides.

Another problem with the use of low melt index polylactide in the outercoating layer of the packaging material is its fairly high meltingpoint, and the resulting poor heat-sealability. As an improvement tothis, US-2002/0065345 A1 discloses a biodegradable aliphatic polyesterthat is blended with polylactide, its portion in the mixture being atleast 9%, and a tackifier, its portion in the mixture being at least 1%.As suitable aliphatic polyesters, the publication mentionspolycaprolactone (PLC) and polybutylene succinate adipate (PBSA).According to the reference, the mixture can be extruded into a film,which can be axially or biaxially stretched, and which can be attachedto the fibre substrate by lamination.

In general, adhesivity to a fibrous base and heat-sealability of PLA maybe improved by blending with selected polymeric additives, but thesehave posed various problems limiting their use. There arenon-biodegradable polymers, which can only be used in small amounts soas not to spoil the overall biodegradability of the PLA-based coatinglayer. Other polymers, which are biodegradable, may be used in largeramounts, but even then problems with runnability on the extrusioncoating machine may limit their use.

US 2014/0147604 A1 teaches that a coating containing at least 70weight-% of polylactide and at least 5 weight-% of polybutylenesuccinate (PBS) or a derivate thereof has an improved adhesion to thefibrous substrate and reduced raw edge penetration (REP). The high shareof 70% or more of PLA is necessary for runnability of the extrusioncoating process in a coating machine. Therefore, there is an upper limitof 30 wt-% for the share of PBS, even though increasing the PBS sharewould otherwise be desirable for further improving heat-sealability.

PLA used for coating fibrous packaging materials has usually been lowmelt index PLA having a melt index at most 25 g/10 min (210° C.; 2.16kg), due to its suitability for extrusion coating. High melt index PLAis too viscous for being extruded as such but may be turned extrudableby blending with other stiffer polymers.

In WO 2010/034712 A1 there are disclosed polymer coatings on a fibrousbase comprising high melt index PLA (NatureWorks 3251 D) blended withpolybutylene adipate terephthalate (PBAT). There may also be an amountof other polyesters such as PBS as further components. Both monolayerand multilayer coatings are described, an example of the latter being astructure comprising innermost and outermost layers of PLA blended withPBAT as well as a middle layer, which is said to be either such a blendor mere PLA. However, the teaching of a middle layer of 100% high meltindex PLA is in practice unworkable. Low melt index PLA should be used,or PLA should be blended with PBAT to turn the material extrudable. In aworking example, the share of PLA in the middle layer is 80% and in theinner and outer layers 60%.

There still remains a need of improving extrudability of the PLA-basedpolymer blend, while securing improved machine speed in extrusion, goodadhesion to the fibrous base, and improved heat-sealing properties ofthe resulting polymer coated fibrous packaging materials. These objectsshould be achieved with improved economy and without compromisingenvironmental aspects of the resulting product.

SUMMARY OF THE INVENTION

The aim of the present inventors was to find an improved method ofpolymer coating of fibrous packaging material. Particularly the aim hasbeen to improve extrudability of a PLA-based polymer blend whilepreserving running speed of the paper or board extrusion coatingmachinery, as well as good adhesivity of the coating to the fibroussubstrate and superior heat-sealability.

The solution according to certain aspects of the present invention isextrusion onto a fibrous substrate one or more polymer coating layersincluding at least one layer of a polymer blend consisting of (i) 20-95wt-% of polylactide having a high melt index of more than 35 g/10 min(210° C.; 2.16 kg), (ii) 5-80 wt-% of polybutylene succinate (PBS) or abiodegradable derivate thereof, and (iii) 0-5 wt-% of one or morepolymeric additives the components of the blend being melted and blendedin connection with the extrusion step.

According to certain aspects of the present invention, extrusion onto afibrous substrate one or more polymer coating layers extruded onto afibrous substrate includes at least one layer of a polymer blendcomprising (i) 20-95 wt-% of polylactide having a high melt index ofmore than 35 g/10 min (210° C.; 2.16 kg), (ii) 5-80 wt-% of polybutylenesuccinate (PBS) or a biodegradable derivate thereof, and (iii) 0-5 wt-%of one or more polymeric additives, the components of the polymer blendbeing melted and blended in connection with an extrusion step.

Blending high melt index PLA with PBS improves extrudability andprovides improved adhesion and heat-sealing properties for the blend.Especially as the polymer components are supplied separately asgranules, which are blended and melted in connection with the extrusionstep, PBS and its derivates have an advantage over PBAT as a blendedcomponent. Use of granules permit easy variation of the shares of thecomponents according to the requirements of individual productionbatches, an advantage over use of premade compounded blends. Use of highmelt index PLA allows raising the share of PBS considerably higher thanwith standard low melt index PLA. As opposed to PBAT, PBS iscommercially available as a product made from renewable, non-fossilraw-materials.

According to a certain embodiment of the present invention, the blend isextruded as an outermost heat-sealable layer of a multilayer coating soas to improve heat-sealability of a coated packaging material. Accordingto another certain embodiment of the present invention, the blend isextruded as an innermost adhesive layer of a multilayer coating so as toimprove adhesion of the coating onto the fibrous substrate.

A preferable embodiment of the present invention comprises coextrusiononto a fibrous substrate a multilayer coating, the multilayer coatingcomprising (i) an innermost layer of a blend comprising 20-95 wt-% ofhigh melt index polylactide and 5-80 wt-% of PBS or its derivate, (ii) amiddle layer containing low melt index polylactide, and (iii) anoutermost layer of a blend comprising 20-95 wt-% of high melt indexpolylactide and 5-80 wt-% of PBS or its derivate.

According to certain aspects of the present invention, a methodcomprises coextrusion onto a fibrous substrate a multilayer coating, themultilayer coating comprising (i) an innermost layer of a blendcomprising 20-95 wt-% of high melt index polylactide and 5-80 wt-% ofPBS or its derivate, (ii) a middle layer containing low melt indexpolylactide, and (iii) an outermost layer of a blend comprising 20-95wt-% of high melt index polylactide and 5-80 wt-% of PBS or itsderivate.

In certain aspects, the polylactide in the innermost and outermostcoating layers is preferably one and the same high melt indexpolylactide. Even in other respects, the components and their shares maybe similar, so that the same polymer blend may be used for both theinnermost and the outermost coating layer, which considerably simplifiesthe coextrusion process.

In the above embodiment, the stiffer layer of low melt index PLA isincorporated as a middle layer of the multilayer structure, to supportlooser high melt index PLA blend layers and thereby improve theircoextrudability. The solution allows sufficient machine speed in thecoextrusion process. Use of standard low melt index PLA improvescontrollability of the extrusion process, while the criticality of theshare of high melt index PLA in the inner and outer layers is reducedand there will be enhanced window for varying the respective blends foroptimal adhesivity and heat-selability. In general, use of high meltindex PLA allows increasing the share of PBS or its derivate in theblend, thereby enhancing heat-sealing and adhesion properties whilepreserving runnability of the extrusion machinery.

In addition to high melt index PLA and PBS or its derivate, at most 5wt-% of other polymeric components may optionally be added to the blend,provided that biodegradability of the coating layer is preserved.Acrylic polymers such as ethylene butyl acrylate glycidyl methacrylateterpolymer (EBAGMA) may be cited as an example of such additives. Atleast a major part of the coating polymers may be produced from rawmaterials obtained from essentially biorenewable natural sources.

Another aspect of the present invention is a biodegradable packagingmaterial. According to certain aspects of the present invention, thematerial comprises a fibrous substrate and one or more extruded polymercoating layers including at least one layer of a polymer blendconsisting of (i) 20-95 wt-% of polylactide having a high melt index ofmore than 35 g/10 min (210° C.; 2.16 kg), (ii) 5-80 wt-% of polybutylenesuccinate (PBS) or a biodegradable derivate thereof, and (iii) 0-5 wt-%of one or more polymeric additives.

In certain other aspects of the present invention, a biodegradablepackaging material comprises a fibrous substrate and one or moreextruded polymer coating layers, the one or more extruded polymercoating layers having at least one layer of a polymer blend comprising(i) 20-95 wt-% of polylactide having a high melt index of more than 35g/10 min (210° C.; 2.16 kg), (ii) 5-80 wt-% of polybutylene succinate(PBS) or a biodegradable derivate thereof, and (iii) 0-5 wt-% of one ormore polymeric additives.

Further aspects of the present invention are a drinking cup, a sealedliquid package, a sealed carton package, and a tray package forready-made food. Characteristic to said products is that they are madeof a packaging material manufactured by the method of the presentinvention or of a packaging material of the present invention asdescribed above. In the case of a disposable drinking cup or a liquidpackage, the polymer coating is lying at least on the innerliquid-contact side of the cup or package. In a tray, the polymercoating covers at least the upper food-contact side of the tray. In acarton package for dry products, the polymer coating may cover the outersurface of the package, protecting the fibrous substrate and the productagainst wetting from the outside. However, in each case, the cup, trayor package may be provided with at least one polymer coating layer onboth sides of the packaging material.

In certain aspects of the present invention, a method of manufacturing abiodegradable packaging material comprises extruding one or more polymercoating layers onto a fibrous substrate, the one or more polymer coatinglayers including at least one layer of a polymer blend having (i) 20-95wt-% of polylactide (PLA) having a high melt index of more than 35 g/10min (210° C.; 2.16 kg), (ii) 5-80 wt-% of polybutylene succinate (PBS)or a biodegradable derivate thereof, and (iii) 0-5 wt-% of one or morepolymeric additives, wherein the components of the blend being meltedand blended in connection with the extrusion step.

In certain aspects of the present invention, the polymer blend consistsof (i) 30-60 wt-% of said high melt index polylactide, (ii) 40-70 wt-%of polybutylene succinate or a biodegradable derivate thereof, and (iii)0-5 wt-% of an acrylic copolymer.

In certain aspects of the present invention, the high melt indexpolylactide has a melt index of 50-100, preferably 70-85 g/10 min (210°C.; 2.16 kg).

In certain aspects of the present invention, the polymer blend isextruded as an outermost heat-sealable layer of a multilayer coating. Incertain other aspects of the present invention, the polymer blend isextruded as an innermost adhesive layer of a multilayer coating.

In certain aspects of the present invention, a multilayer coatingcomprises an innermost layer, a middle layer containing polylactidehaving a low melt index of 5-35 g/10 min (210° C.; 2.16 kg), and anoutermost layer, wherein the innermost layer and the outermost layercomprise a polymer blend having (i) 20-95 wt-% of polylactide (PLA)having a high melt index of more than 35 g/10 min (210° C.; 2.16 kg),(ii) 5-80 wt-% of polybutylene succinate (PBS) or a biodegradablederivate thereof, and (iii) 0-5 wt-% of one or more polymeric additives.In certain aspects, the components of the blend are melted and blendedin connection with an extrusion step. In certain other aspects of thepresent invention, the innermost and the outermost layer of themultilayer coating is the same.

In certain aspects of the present invention, a monolayer coating isextruded into direct contact with the fibrous substrate.

In certain aspects of the present invention, the machine speed inextrusion is at least 100 m/min, in some aspects at least 150 m/min, insome other aspects at least 200 m/min, and in some other most preferableaspects at least 250 m/min.

In certain aspects of the present invention, a biodegradable packagingmaterial comprises a fibrous substrate and one or more extruded polymercoating layers including at least one layer of a polymer blend having(i) 20-95 wt-% of polylactide having a high melt index of more than 35g/10 min (210° C.; 2.16 kg), (ii) 5-80 wt-% of polybutylene succinate ora biodegradable derivate thereof, and (iii) 0-5 wt-% of one or morepolymeric additives.

In certain aspects of the present invention, the packaging materialcomprises a fibrous substrate and an extruded multilayer coatingincluding innermost and outermost layers of a polymer blend, theinnermost and outermost polymer blend layers being (i) 30-60 wt-% ofpolylactide having a high melt index of 50-100 g/10 min (210° C.; 2.16kg), (ii) 40-70 wt-% of polybutylene succinate or a derivate thereof,and (iii) 0-5 wt-% of an acrylic copolymer, and a middle layer ofpolylactide having a low melt index of 5-35 g/10 min (210° C.; 2.16 kg).

In certain aspects of the present invention, the polymer blend layer isprovided on the inner liquid-contact side of a drinking cup. In someother aspects, the polymer blend layer is provided on a liquid-contactside of a sealed liquid package. In some other aspects, the polymerblend layer is provided on the outside of a sealed carton package. Instill some other aspects, the polymer blend layer is used in a traypackage for ready-made food, with the polymer blend layer on thefood-contact side of the tray.

The above summary of the various representative aspects and embodimentsof the present invention is not intended to describe each illustratedaspect or embodiment or every implementation of the present invention.Rather, the aspects and embodiments are chosen and described so thatothers skilled in the art can appreciate and understand the principlesand practices of the present invention. The figures in the detaileddescription that follow more particularly exemplify these aspects andembodiments.

BRIEF DESCRIPTION OF THE FIGURES

The invention can be completely understood in consideration of thefollowing detailed description of various aspects and embodiments of thepresent invention in connection with the accompanying drawings, inwhich:

FIG. 1 is a schematic presentation of coating machine speeds(runnability) obtained in various comparative materials and embodimentsaccording to the present invention.

FIG. 2 is a schematic presentation of adhesion properties obtained invarious comparative materials and embodiments according to the presentinvention.

FIG. 3 is a schematic presentation of heat-sealing properties obtainedin various comparative materials and embodiments according to thepresent invention.

FIG. 4 is a schematic summary of properties of three-layered structuresaccording to the present invention.

FIG. 5 compares schematically the properties of comparative monolayeredstructures and three layered structures according to the presentinvention.

FIGS. 6a-6e show as examples structural embodiments of the packagingmaterial according to the present invention.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

The present invention is based on a surprising finding thatextrudability of a PLA-based polymer blend at an extrusion coatingmachine producing the packaging material can be improved while runningspeed of the machine, as well as, heat sealability of the polymer-coatedmaterial may be preserved by using PLA having a high melt index of morethan 35 g/10 min (210° C.; 2.16 kg) as a polymer blend with polybutylenesuccinate (PBS) or its biodegradable derivate, e.g. poly(butylenesuccinate adipate) (PBSA).

As an overall rule, the melt index and the molecular weight (MW) of PLAare in reverse ratio to each other, i.e. as the melt index increases theMW decreases. In general, the high melt index PLA as used in the presentinvention has a MW of less than 160 000, preferably about 100 000. Thelow melt index PLA as used in multilayer embodiments of the presentinvention has a MW of at least 160 000, and preferably about 200 000.

A multilayer coating may be produced by extruding onto a fibroussubstrate inner, middle and outer coating layers. The inner and outerlayers contain a blend comprising polylactide having a melt index >35g/10 min (210° C.; 2.16 kg) and PBS or its derivate. Optionally theblend may comprise even other components, for instance acryliccopolymers, which shall not destroy the overall biodegradability of thecoating layer, however.

The fibrous substrate in the packaging material may be paper or board,paper-board as well as cardboard.

Amount of said polylactide having a melt index >35 g/10 min in saidblend is 20-95 wt-%, preferably 30-60 wt-%.

Melt index of said polylactide is >35 g/10 min, preferably >40 g/10 min,and more preferably 50-100 g/10 min, still more preferably 60-90 g/10min, and most preferably even 70-85 g/10 min (210° C.; 2.16 kg). Theinventors have demonstrated that PLA having high melt index allowsblending of a higher share of another biodegradable polymer such aspolyester to the coating and allows using higher machine speeds in theextrusion process.

Up to now, the PLA used for coating fibrous substrates has in most caseshad a molecular weight of about 200 000 g/mol and a melt index at mostabout 25 g/10 min (210° C.; 2.16 kg). Within the meaning of the presentinvention, the phrase “high melt index PLA” refers to PLA with a meltingindex, which is more than 35 g/10 min (210° C.; 2.16 kg), and amolecular weight reduced, preferably by at least about 40%, compared totraditionally used low melt index PLA.

Further, PLA can be produced by using renewable starting material. It isalso biodegradable e.g. in composting and can be burned.

Within the meaning of the present invention, the term “biodegradable”means polymers that will decompose in natural aerobic (composting) andanaerobic (landfill) environments. Biodegradation of polymers occurswhen microorganisms metabolize the polymer to either assimilablecompounds or to humus-like materials that are less harmful to theenvironment. They may be derived from renewable raw materials, orpetroleum-based plastics which contain additives. Aromatic polyestersare almost totally resistant to microbial attack, most aliphaticpolyesters are biodegradable due to their potentially hydrolysable esterbonds. Polybutylene succinate (PBS) is an examples of such biodegradablepolyesters.

Especially PLA used in the present invention may be of natural origin,i.e. manufactured from renewable natural resources such as corn, potato,tapioca, cellulose, soy protein, lactic acid etc., or can be naturallyproduced (e.g. by microbial fermentation), and is biodegradable orcompostable. Also, PBS and its derivates, such as PBSA, arebiodegradable or compostable, but may even be of fossil (petroleum)origin.

Amount of PBS or its derivate in the blend is 5-80 wt-%, preferably40-70 wt-% and most preferably 45-65 wt-%. Preferably the polymer isPBS, which improves the adhesion properties of the coating layer as wellas heat-sealablility.

Within the meaning of the present invention, term “adhesion” meansadhesion to any surface including fibrous material and polymer coatedsurface but particularly it means adhesion to raw fibrous material(paper or board) constituting the fibrous substrate. The aim is toachieve complete adhesion, which means that an attempt to detach thecoating results in breaking within the fibrous substrate layer, insteadof the coating peeling off as a whole.

Within the meaning of the present invention, the term “heat-sealability”means that the polymer coating in softened or melted condition may beattached to an opposite surface of material, which may be the same oranother polymer, raw fibrous material etc. A firm seal between thesurfaces is formed as the heated polymer cools down and solidifies. Whena polymer blend is used in accordance with the invention an acceptableheat-sealing can be achieved within a broader temperature range than incase PLA alone is used.

A major advantage of the method according to the present invention isimproved runnability of the coating machinery, i.e. sufficient extrusionand adhesion properties allow using a high machine speed in spite of useof the high melt index PLA.

In the method, the machine speed in extrusion is at least 100 m/min.Preferably the machine speed is at least 150 m/min, more preferably atleast 200 m/min, still more preferably at least 250 m/min and mostpreferably at least 300 m/min. The high machine speed improves theeconomy of the manufacturing process.

As a preferable third component, the blend may comprise a minor amount,at most about 5% by weight, an acrylate copolymer, such as ethylenebutyl acrylate glycidyl methacrylate terpolymer (EBAGMA). The packagingmaterial of the present invention may thus comprise a coating layerconsisting of a blend of (i) 30 to 60 weight-% of high melt index PLA,(ii) 40 to 70 weight-%, of PBS or its derivate, and (iii) 0 to 5weight-% of an acrylate copolymer.

The acrylate polymer is added to further improve the adhesion of theextruded polymer coating layer to the fibrous substrate. Acrylatepolymers, including EBAGMA, are as such non-biodegradable, but when usedin small amounts of 5 weight-% at most do not prevent disintegration ofthe coating layer as a whole.

According to the present invention, the preferred biodegradable polymerblended with PLA is polybutylene succinate (PBS). The specific advantageof PBS is superior blendability with high melt index PLA in theextruder, into which PBS and PLA granules may be fed separately.

PBS, or its derivate, blended with PLA improves adhesion of a coatinglayer consisting of the blend in extrusion onto a fibrous boardsubstrate. At the same time, raw edge penetration of liquid in drinkingcups made of the coated packaging material according to the presentinvention is significantly reduced in comparison with PLA alone, whichin case of hot coffee is seen as markedly less, if any, brown colouringalong the vertical heat-seal lines in the cup jacket. The improvedadhesion is also supposed to increase the ability of the coating towithstand the vapour pressure generated within the fibrous substrate bythe hot drink, thus preventing the coating from loosening from thesubstrate layer and opening pathways to liquid penetration.

In addition to good adhesion and heat-sealing properties andextrudability as PLA blends, PBS and derivates such as PBSA arebiodegradable and the blend can be manufactured predominantly from rawmaterials obtained from renewable natural sources.

A biodegradable polymer blend as discussed above may advantageously beextruded as the uppermost surface layer of the coated packagingmaterial. In this case, PBS or its derivate serves to improve theheat-sealability of the polymer coated packaging material. Addition of aminor amount of acrylate copolymer, such as EBAGMA, further improvesheat-sealability of the coating layer.

A biodegradable polymer blend as discussed above may advantageously beextruded into a direct contact with the fibrous substrate of thepackaging material. Due to good adhesion properties there is no need touse separate adhesion layers between the fibrous substrate and thecoating of the present invention. This simplifies the manufacturingprocess and reduces raw material costs. PBS or its derivate serves toimprove adhesion of the coating layer to the underlying fibroussubstrate. In the multilayer coating, said coating layer is thelowermost layer.

In the coextruded multilayer coating, each layer should substantiallyconsist of biodegradable polymers, which preferably are based onrenewable raw materials. The material may have a polymer coating on oneside or on both sides thereof. The coatings on the opposite sides of thefibrous substrate may be similar or differ from each other, for instancea multilayer coating on one side and a monolayer coating on the oppositeside.

According to the present invention, the components of the blend aremelted and blended in connection with the extrusion step, morespecifically the components of the polymer blend are mixed as granulesand melted at a single step, immediately followed by extrusion of themelt onto a paper or board substrate. This works especially well withPLA and PBS or its derivate. Mixing of the components first in theextruder allows easy adjustment of the respective shares of thecomponents being mixed, an advantage over use of premade compoundedblends. Availability of granulate PLA and polyesters is good andtypically also the price is lower compared to pre-mixed blends.

The total amount of polymer coating on one side of the fibrous substratemay be in the range of 10-60 g/m², typically about 25 g/m². In amultilayer coating the amount of polymer per layer may be 4-20 g/m²,preferably 6-15 g/m². A representative example could be a triple layercoating with a middle layer of solely low melt index PLA and coatinglayer weights of 7, 11 and 7 g/m², respectively.

A useful embodiment of the present invention is a packaging materialcomprising a fibrous substrate and one or more extruded polymer coatinglayers including at least one layer of a polymer blend consisting of (i)20-95 wt-% of polylactide having a high melt index of more than 35 g/10min (210° C.; 2.16 kg), (ii) 5-80 wt-% of polybutylene succinate (PBS)or a biodegradable derivate thereof, and (iii) 0-5 wt-% of one or morepolymeric additives.

A preferred embodiment of the present invention is a fibrous paper orboard-based packaging material comprising coextruded inner, middle andouter coating layers, the inner and outer layer comprising a blend of20-95 wt-% of PLA having a melt index of above 35 g/10 min (210° C.;2.16 kg), 5-80 wt-% of PBS or its biodegradable derivate and,optionally, 0-5 wt-% of an acrylic copolymer such as EBAGMA, and themiddle layer comprising polylactide having a melt index of 5-35 g/10 min(210° C.; 2.16 kg). The inner layer would provide superior adhesion inextrusion to the fibrous substrate and the outer layer would providesuperior heat-sealability to an uncoated fibrous surface or to a polymerlayer, similar or dissimilar to said outer heat-seal layer itself.Middle layer containing PLA with low melting index supports the polymerlayers during extrusion process. PLA is also renewable and usefulmaterial having e.g. good moisture barrier properties as well as lowcost. Multilayered structure allows optimizing the raw material withoutcompromising the extrudability or properties of the resulting coating.

In a more preferred embodiment, said packaging material comprises afibrous substrate and an extruded multilayer coating including innermostand outermost layers of a blend of 30-60 wt-% of polylactide having amelt index of 50-100 g/10 min (210° C.; 2.16 kg), 40-70 wt-% of PBS orderivate, and 0-5 wt-% of an acrylic copolymer, and a middle layer ofpolylactide having a melt index of 5-35 g/10 min (210° C.; 2.16 kg). Thesame blend is advantageously used for the innermost and outermostlayers.

The present invention further provides improved containers made of thepackaging material as described above. Disposable drinking cups for hotdrinks, especially hot coffee, are a prime example of such containers.

According to the present invention, a drinking cup made of a packagingmaterial manufactured by the method of the present invention, or of apackaging material of the present invention, has the polymer coatinglying on the inner liquid-contact side of the cup.

According to the present invention, a sealed liquid package of apackaging material manufactured by the method of the present invention,or of a packaging material of the present invention, has the polymercoating lying on the inner liquid-contact side of the package. However,a similar package may even be used as a carton package for dry products.

According to the present invention, a sealed carton package of apackaging material manufactured by the method of the present invention,or of a packaging material of the present invention, may have thepolymer coating lying on the outside of the package.

According to the present invention, a tray package for ready-made food,the tray being made of a packaging material manufactured by the methodof the present invention, or of a packaging material of the presentinvention, has the polymer coating lying on the food-contacting upperside of the tray.

The product packages according to the present invention are preferablycompletely made of the packaging material as described above. In eachcase even the reverse side of the packaging material may bepolymer-coated, e.g. for improving heat-sealability or for gas or aromabarrier purposes.

EXAMPLES

FIGS. 6a-6e show as examples five structural embodiments of packagingmaterials according to the present invention. “PLA1” means low meltindex PLA; “PLA2” means high melt index PLA; “PBS” means polybutylenesuccinate and “board” indicates the fibrous substrate layer, which ispaper, paperboard or cardboard. Instead of PBS, even biodegradablederivates of PBS may be used.

There are extruded or coextruded monolayer or multilayer coatings of ablend of PLA2 and PBS and mere PLA1 on one side or on both sides of afibrous paper or board substrate (“board”). The share of PLA2 in theblend is 20 to 95 weight-%, preferably 30 to 60 weight-%, and the shareof PBS may vary from 5 to 80 weight-%, preferably being 40 to 70weight-%. As an optional third component at most 5 weight-% of anacrylate copolymer such as ethylene butyl acrylate glycidyl methacrylateterpolymer (EBAGMA) may be included in the blend. The substrate may bepaper, paperboard or cardboard of a weight of 40 to 350 g/m², preferablya cupboard or a liquid package board of 170 to 350 g/m².

It is understood by a skilled reader that if the packaging material hasextruded polymer coatings on both sides, the coatings on the oppositesides need not be identical. There may be a mono-layer coating on oneside and a multilayer coating on the other side of the fibroussubstrate. It is also possible to include in multilayer coatings layersof other biodegradable polymers suitable for extrusion coating,preferably in blends with high melt index polylactide.

Usefully PBS is available as a commercial product under trade name GsPLAFZ91PD by Mitsubishi, and EBAGMA is commercially available under tradename Biomax Strong 120 by DuPont.

More particularly, FIG. 6a shows the substrate 1 with a single extrudedcoating layer 2 of the blend of PLA2 and PBS. The weight of thismonolayer 2 may be from 10 to 30 g/m². In FIG. 6b there is such aPLA2+PBS blend layer 2 on both sides of the substrate 1.

FIG. 6c shows a coextruded multilayer coating with an innermost PLA2+PBSblend layer 2, a middle layer 3 of PLA1, and an outermost PLA2+PBS blendlayer 4. The weight of each of the three layers 2, 3, 4 may be from 4 to13 g/m². The total weight of the multilayer coating is thus 12-39 g/m².Including a middle layer 3 of PLA1 serves to add to the total thicknessof the coating while improving its extrudability. FIG. 6d shows similarmultilayer coatings 2, 3, 4 on both sides of the substrate 1.

FIG. 6e shows a packaging material comprising a board substrate 1 andcoextruded innermost, middle and outermost coating layers 2, 3, 5. Onlythe innermost layer 2 consists of a PLA2+PBS blend as described above.The middle layer 3 consists of mere PLA1. The outermost heat-sealinglayer 5 comprises a blend of about 45 weight-% of PLA2 and 55 weight-%of polybutylene adipate terephtalate (PBAT). The weights of the threecoating layers 2, 3, 5 may correspond to the respective layers 2, 3, 4in the embodiment of FIG. 6 c.

If the packaging material has extruded polymer coatings on both sides,the coatings on the opposite sides need not be identical. There may be amonolayer coating on one side and a multilayer coating on the other sideof the fibrous substrate. It is also possible to include in multilayercoatings layers of other biodegradable polymers suitable for extrusioncoating, preferably in blends with PLA2. FIG. 6e is an example of suchembodiments. In addition to PBAT, other examples of useful polymers arePHA (polyhydroxy alkanoate), PHB (polyhydroxy butyrate), PHBV(polyhydroxybutyrate hydroxyvalerate), PGA (polyglycolic acid), PEG(polyethylene glycol), PCL (polycaprolactane), and starch basedbiopolymers. The innermost layer of the multilayer structure shall be ofthe blend containing PLA and PBS or its derivate, however.

Tests

In the following, the present invention is illustrated by means oflaboratory tests. Extrusion grade polylactides having “low” or “high”melt indexes (see Table 1 below) and polybutylene succinate (PBS) wereused as coating polymers as such or blended as shown in Table 2. Theblends as well as pure PLA (used also as a reference) were then extrudedas monolayers or as three layered structures onto one side of a boardsubstrate having a weight of 280 g/m². True coating weights in bothmonolayer and three layer structures were measured. Due to the coatingtechniques they varied slightly, between 24.9 and 27.6 g/m² (about 25g/m²).

TABLE 1 Characteristics of the polymers used in experimental part.Polymer melting index temperature PLA1 25 g/10 min; 210° C. “low” PLA275 g/10 min; 210° C. “high” PBS 4.5 g/10 min 190° C.

For each coated test material the runnability of the coating machine andadhesion and heat-sealing properties of the resulting coating weremeasured.

Adhesion to the board substrate was determined on a scale from 0 to 5,the highest figure representing the best adhesion. The polymericcoatings were thus introduced onto the substrate by extrusion, and theiradhesion to the board surface was defined on said scale, whereby theclassification was as follows:

1=no adhesion, the polymeric layer peels off;

2=poor adhesion, some fibres are stuck to the polymeric layer that peelsoff;

3=poor adhesion, when detaching the polymeric layer, less than 50% ofthe paper board breaks in the area of coating;

4=moderate adhesion, when detaching the polymeric layer, over 50% of thepaper board breaks in the area of coating;

5=perfect adhesion, when detaching the polymeric layer, the paper boardbreaks throughout the area of coating.

Heat-sealability is given as the lowest sealing temperature providingsuccessful sealing between the heat-seal layer and a countersurface, inthe tests the heat-seal layer itself. The criterium is that an attemptto tear open the seal results in a break in the fibrous board substrateinstead of opening of the seal.

Runnability is given as the lowest operable machine speed in extrusionor coextrusion.

TABLE 2 The adhesion, heat-sealablity and runnability (coating machinespeed) results of monolayer and three layer coatings applied on boardsubstrate. PLA1 is conventionally used PLA having melt index (about 25g/10 min) and PLA2 has high melt index (about 75 g/10 min). Column atright, when appropriate, refers to the general structure as shown inFIG. 6. Heat- sealability Runnability Adhesion (° C.) (m/min) FIG.Board/10% PBS + PLA1 4 440 290 Board/15% PBS + PLA1 — — — Board/20%PBS + PLA1 — — — Board/20% PBS + PLA2⁽¹⁾   4.5 380 100 6a Board/40%PBS + PLA2⁽¹⁾   4.5 400 240 6a Board/60% PBS + PLA2⁽¹⁾ 4 410 100 6aBoard/20% PBS + PLA1/PLA1/20% PBS + PLA1 5 460 250 Board/40% PBS +PLA1/PLA1/40% PBS + PLA1 — — — Board/60% PBS + PLA1/PLA1/60% PBS + PLA1— — — Board/80% PBS + PLA1/PLA1/80% PBS + PLA1 — — — Board/20% PBS +PLA2/PLA1/20% PBS + PLA2⁽¹⁾ 5 410 270 6c Board/40% PBS + PLA2/PLA1/40%PBS + PLA2⁽¹⁾ 5 410 320 6c Board/60% PBS + PLA2/PLA1/60% PBS + PLA2⁽¹⁾ 5380 300htd 6c Board/80% PBS + PLA2/PLA1/80% PBS + PLA2⁽¹⁾ 4 360 300 6cBoard/PLA2/PLA1/PLA2 4 390 220 Board/PBS/PLA1/PBS 4 350 200 Board/PBS 4350 180 Board/PLA2 3 390 poor ⁽¹⁾signifies examples according to theinvention, the other examples are comparative.

Lack of result implies failure in testing and thus unworkability.

The runnability results (coating machine speed) are shown in FIG. 1. Itwas proved that the machinery was unable to handle high (>40%) PBSconcentrations by using conventional PLA (PLA1) whereas replacingconventional PLA (PLA1) with high melt index PLA (PLA2) and/or 3-layerstructure (PLA1 layer in the middle and PLA2+PBS in inner and outerlayer) resulted in superior runnability. Also monolayered structureusing PLA2, especially when blended with 40% of PBS, had goodrunnability. Coating could not be successfully done solely with PLA2.

The adhesion results are shown in FIG. 2. In each case use of high meltindex PLA in combination with PBS improved the adhesion value. Noimprovement was detected after 20% PBS concentrations.

Heat-sealability results are shown in FIG. 3 and show that using highmelt index PLA the heat-sealability is significantly improved, c.f. thelower heat-sealing temperatures. In addition it was found that a blendcomprising high melt index PLA and PBS can be heat-sealed in a broadtemperature range thereby providing flexibility to process (data notshown).

The three layered coating structures (FIG. 6c ), where PLA1 is used inthe middle layer and PLA2 is blended with PBS in the innermost andoutermost layers, were found to be especially beneficial by enabling thehighest coating machine speed (runnability) and excellent heat-sealingand adhesion properties. It is believed that PLA1 in the middle layergives rigidity to film.

Although specific examples have been illustrated and described herein,it will be appreciated by those of ordinary skill in the art that anyarrangement calculated to achieve the same purpose could be substitutedfor the specific examples shown. This application is intended to coveradaptations or variations of the present subject matter. Therefore, itis intended that the present invention be defined by the attached claimsand their legal equivalents, as well as the following illustrativeembodiments.

The invention claimed is:
 1. A biodegradable packaging material,comprising: a multilayer coating extruded on a fibrous substrate, saidextruded multilayer coating having a non-aromatic innermost layer, anoutermost layer, and a middle intermediate layer between saidnon-aromatic innermost and outermost layers, said non-aromatic innermostlayer consisting of (i) 30-60 wt-% of polylactide having a high meltindex of 50-100 g/10 min (210° C.; 2.16 kg), (ii) 40-70 wt-% ofpolybutylene succinate or a derivate thereof, and (iii) greater than 0wt-% up to 5 wt-% of said ethylene butyl acrylate glycidyl methacrylateterpolymer, and said middle intermediate layer consisting of polylactidehaving a low melt index of 5-35 g/10 min (210° C.; 2.16 kg).
 2. Thebiodegradable packaging material of claim 1 in the form of a drinkingcup having an inner liquid-contact side, said non-aromatic innermostlayer located on the inner liquid-contact side of the cup.
 3. Thebiodegradable packaging material of claim 1 in the form of a sealedliquid package having an inner liquid-contact side, said non-aromaticinnermost layer located on the inner liquid-contact side of the sealedliquid package.
 4. The biodegradable packaging material of claim 1 inthe form of a sealed carton package having an outside, said non-aromaticinnermost layer located on the outside of the sealed carton package. 5.The biodegradable packaging material of claim 1 in the form of a traypackage for ready-made food having at least one food contact side, saidnon-aromatic innermost layer located on said at least one food contactside of the tray package.
 6. The biodegradable packaging material ofclaim 1, wherein said outermost layer being non-aromatic, saidnon-aromatic outermost layer consisting of (i) 30-60 wt-% of polylactidehaving a high melt index of 50-100 g/10 min (210° C.; 2.16 kg), (ii)40-70 wt-% of polybutylene succinate or a derivate thereof, and (iii)greater than 0 wt-% up to 5 wt-% of said ethylene butyl acrylateglycidyl methacrylate terpolymer.